Observed temperature changes in Emilia-Romagna: mean values and extremes

Abstract

Temporal and spatial variability of temperature in Emilia-Romagna is described using daily maximum and minimum temperature at 40 stations covering the period 1958 to 2000. Before use, data were quality controlled and tested for inhomogeneity using standard techniques. First, a description of climatological values of maximum and minimum temperature and of their temporal variability is given. Then, frequency of extreme events in temperature is described using 4 indices: 10th percentile of minimum temperature, 90th percentile of maximum temperature, number of frost days and heat wave duration. These indices are based on daily temperature and were computed for all seasons. For each season and each index, the magnitude of trends was estimated by linear regres- sion, while statistical significance was evaluated by Kendall's τ. The analysis reveals the presence of an increase in mean maximum and minimum temperature, especially during winter and summer. Trends were significant in the plain and hill area. Similar tendencies were also observed in the 10th percentile of daily minimum temperature in both seasons, accompanied by a reduction in the num- ber of frost days during winter. Positive trends were detected in the 90th percentile of daily maximum temperature during winter, spring and summer, leading to an increase in the heat wave duration index. These results were significant over almost the whole region, summer being the season charac- terised by the greatest number of stations with significant trends. The spatial variability of frequency of extreme events was analysed using cluster techniques. Finally, the relationship between winter frequency of extreme temperature events in Emilia-Romagna and large-scale Euro-Atlantic circula- tion patterns is briefly described. The results show the presence of significant values of correlation with some of the patterns considered, namely the Eastern Atlantic and European Blocking pattern.